ASLAN, A., R. A. MORTON, W. A. WHITE, J. A. RANEY, and E. H. GUEVARA
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Abstract: Geologic Framework of the Holocene Orinoco Delta, Venezuela

Compared with that of other large deltaic systems, the geology of the Orinoco Delta of Venezuela is poorly known. A five-year study is under way to characterize the modern delta and provide baseline information for monitoring changes as hydrocarbon exploration commences in the region.

The Orinoco Delta exhibits a variety of landforms and processes that are attributable to (1) large water and suspended sediment discharges, (2) longshore currents that supply suspended sediment derived from the Amazon River, (3) tidal ranges of as much as 2.5 m, (4) a tropical climate and high rates of biologic productivity and organic sedimentation, and (5) proximity to the Caribbean-South American plate boundary. These factors create three subregions of the lower delta plain. The southeastern third is dominated by the principal flow of the Orinoco River and tidal processes. Fluvialmarine interactions produce a complex network of anastomosing channels separated by mangrove-covered islands. The shoreline of the northeastern third is prograding in response to sediment supplied by distributary channels and northwesterly directed longshore drift, which produces extensive mangrove-covered mud capes. The northwestern third is experiencing coastal erosion, widespread peat development, and lateral infilling of a large distributary channel, which is due to dam construction.

Geomorphic evidence indicates that the Orinoco River has been confined to the southern part of the delta during the Holocene, whereas distributary channels of the northern delta have avulsed frequently. Distributary channels, not the mainstem Orinoco, have constructed about two-thirds of the delta plain. Lastly, a discontinuous belt of beach-ridge complexes and marshy savanna located parallel to and ~20 to 50 km inland from the coast is elevated relative to surrounding delta plain and may reflect regional neotectonism.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas